Alkylation processes and, in particular, processes for the alkylation of aromatics are of considerable importance on the industrial scale for the production of basic chemicals. Thus, the alkylation of benzene with ethylene and propylene to produce ethylbenzene and cumene is for example widely used in the petrochemical industry. In this respect, cumene is an important chemical intermediate mainly used for the production of phenol and acetone, whereas ethylbenzene is an intermediate used in the production of styrene. In addition to these, long chain alkylbenzenes are useful as lubricant base stocks and as intermediates in the production of detergents.
For the production of such basic chemicals Lewis and Bronsted acids are typically used, such that a variety of zeolites are commonly employed as alkylation catalysts. Thus, alkylation of aromatic hydrocarbon compounds employing certain crystalline zeolite catalysts is known in the art. In this respect, alkylation of benzene with ethylene and propylene in the presence of zeolite catalysts represents the preferred commercial techniques for the production of ethylbenzene and cumene.
However, along with the desired monoalkylated products, typical alkylation processes produce di- and tri-alkylated products, in addition to oligomers and other side-products. As a result of this, time and cost intensive separation processes must normally be employed for obtaining an alkylation product which is sufficiently pure to be used as a feed in the production of the follow-up products.
Accordingly, considerable efforts have been made for developing processes and catalysts affording higher selectivities for the monoalkylation products in order to increase the effectiveness of the known industrial processes.
In this respect, U.S. Pat. No. 7,569,739 B2 for example relates to aromatics alkylation, and in particular to the alkylation of benzene with ethylene and propylene to produce ethylbenzene and cumene, respectively. Furthermore, said document is concerned with the alkylation of aromatics with long chain alkylating agents to produce the corresponding long chain alkylbenzenes. In the alkylation reactions, zeolitic materials, and in particular zeolitic materials having the MWW framework structure are used. In particular, relates to a means of enhancing the selectivity of the alkylation reaction towards monoalkylated products by modifying the zeolitic materials with phosphorous.
U.S. Pat. No. 7,348,465 B2 specifically relates to the alkylation of benzene with propylene and butenes, especially for the production of feedstocks used for producing follow-up chemicals such as cumene and s-butylbenzene. In particular, said document aims at providing a method for enhancing the selectivity of aromatic alkylation to monoalkylated species. To this effect, the use of molar blends of propylene and one or more linear butenes are taught therein. A clear drawback to said method, however, resides in the fact that it is highly limited both with respect to the alkylatable organic compounds and to the alkylating agents which may used therein, in addition to the fact that only mixtures of monoalkylated products may be obtained.
In Bellussi et al., Journal of Catalysis 1995, 157, pp. 227-234, the activity and selectivity of various zeolites including zeolite Beta in the alkylation of benzene catalyzed by the former is discussed, in particular with respect to the respective reactions of ethylene and propylene with benzene. In this respect, Bellussi et al. report on an increase in both the conversion rate and the selectivity of zeolite Beta in said alkylation reaction with decreasing Si/Al molar ratio of the zeolite Beta used therein. However, as may be taken from the results disclosed in said document, the moderate increase in selectivity for the monoalkylated species with descreasing Si/Al molar ratio of the zeolite Beta materials is accompanied by a comparatively greater increase in di- and trialkylation products. The corresponding observation is almade in Halgeri et al., Applied Catalysis A: General 1999, 181, pp. 347-354, wherein the effect of dealumination of zeolite Beta on its activity and selectivity in the alkylation of aromatics is discussed. In particular, regarding the selectivity of zeolite Beta towards dialkylation products in the reaction of benzene with isopropanol, the results displayed in said document show a decrease in said selectivity with increasing dealumination of the zeolite Beta material used in the reaction.
Finally, regarding further alkylation reactions catalyzed by zeolite Beta, Yoon et al., Journal of Catalysis 2006, 245, pp. 253-256, for example relates to the trimerization of isobutene over a zeolite Beta catalyst. Tang et al. in “From Zeolites to Porous MOF Materials—the 40th Anniversary of International Zeolite Conference”, Studies in Surface Science and Catalysis 2007, pp. 1454-1459, on the other hand, concerns the tert-butylation of phenol over zeolitic materials including H-zeolite Beta.
There however remains a need to improve the selectivity of alkylation reactions, in particular in view of a time and cost-effective method for providing high purity feedstocks of a wide variety of basic chemicals employed in large scale industrial production processes.